Print hammer anti-rebound mechanism



Aug. 4, 1964 C. H. VANN PRINT HAMMER ANTI-REBOUND MECHANISM Filed Oct. 11, 1962 INVENTOR COURTNEY H. VANN HIS ATTORNEYS United States Patent 3,143,964 PRINT HAMMER ANTI-REBOUND MECHANHSM Courtney H. Vann, Ithaca, N.Y., assignor to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Oct. 11, 1962, Ser. No. 229,907 6 Claims. (Cl. 101-93) This invention relates generally to an improvement in means to prevent rebound of print hammers used in cash registers, calculating, and like machines. More particularly, the invention relates to an improved anti-rebound mechanism adapted to spring-actuated impression or print hammers of the kind used in machines of the type shown and described in United States Letters Patent No. 2,666,- 574, issued to Carl H. Carlson et al., on January 19, 1954.

In the printer construction shown and described in such Carlson et al. patent, the essential portion of which is further illustrated and described herein, the print hammer is actuated by a powerful spring, which when released, forces the hammer against a type carrier with a sudden blow. With such construction, when the hammer completes its full printing stroke, it reacts against the driving spring, which tends to cause such hammer to rebound, and in some instances, this rebound is of suficient magnitude to cause a second or ghost impression to be made. As can be understood from the patent to Shipley, No. 1,652,057; the patent to Robertson, No. 2,117,451; and the patent to Williams et al., No. 2,625,100, as examples, numerous means have been devised to prevent (both through dampening and latching) spring-actuated print hammers from rebounding after making a printing stroke. All of such mechanisms, while being effective in their performance of the desired task, comprise not only a plurality of parts, but require definite space commitments to be made therefor in the overall pninter construction. This, of course, adds both to the problems of assembly and to the cost factor of a machine employ ing same. Contrary to this, in the present application a single latch pawl is operably associated in such a way with a spring-actuated print hammer that any possible rebound thereof is positively prevented after each printing stroke, thereby avoiding blurred impressions caused by an overprinting due to the hammer striking the type carrier the second time.

Thus, the principal object of this invention is to provide an extremely simple, yet very effective mechanism to prevent rebound of spring-actuated print hammers.

A further object of the invention is to provide such a mechanism which, without the use of any great number of tools and the like, may be quickly and easily adapted to printer constructions employing either print hammers or printing platens of the spring-actuated type.

Still a further object of the instant invention is to provide such a mechanism of extremely low cost, both in its manufacture and in its assembly both to new and inservice machines.

With these and incidental objects in view, the invention includes certain novel features of construction and combinations of parts, the essential elements of which are set forth in appended claims and a preferred form or embodiment of which is hereinafter described with reference to the drawing which accompanies and forms a part of this specification.

Of said drawing:

FIG. 1 is a side elevation of a printer unit of the spring-actuated hammer type embodying the instant invention, the hammer being illustrated therein in the position which it assumes just before being released for a printing stroke;

FIG. 2 is a detail side view of the print harruner of FIG.

1 as associated with the instant invention when at the end of a printing stroke; and

FIG. 3 is a detail side view of the print hammer of FIG. 1 as associated with the instant invention immediately after the completion of a printing stroke.

General Printer Mechanism While the present application illustrates only one print hammer 10, as known from the above-mentioned reference patent to Carlson et al., any number of same may be provided in a side-by-side order, each being rockably carried by a support shaft 11 extending between a pair of printer side frames 12 (one frame only shown herein), and each being aligned with the upper end portion of an associated type bar 13. As understood from FIG. 1, such type bar 13 is movable vertically in slotted guides 14 and 15 with respect to a resilient paper platen 16. As illustrated in FIGS. 1, 2, and 3, the upper end portion of such type bar 13 carries a plurality of individual type members 17. As usual, the lower end portion of such type bar 13 is pivoted to a machine carried differential mechanism (not illustrated herein) so that the digit value being entered into the machine may be represented by a particular type member 17 being moved to a printing position with respect to the paper platen 16. The actual printing operation is then performed as such type member 17 is struck by its associated print hammer 10 (as illustrated in FIG. 2) when released from a cocked position (as illustrated in FIG. 1) at a precise printing time determined by the tripping of a hammer latch 18 during machine operation.

Referring to FIG. 1, when the type bar 13, under control of the interconnected differential mechanism, is caused to be raised for presenting a particular type member 17 thereof to printing position, all as described in detail in the hereinabove-referred-to reference Patent No. 2,666,- 574, a stud 19 thereon enables an interponent 29 to rock counter-clockwise on a bail 21 under urge of a spring 22. The bail 21 extends between an operating arm 23 and another operating arm, like the arm 23, secured on the outer ends of the print hammer support shaft 11, extending between the printer side frames 12.

Operation of a machine of the type herein referred to is through suitable rocking of a machine rear drive shaft 24, such as by means of an electric motor or operating handle, which shaft 24 is caused to oscillate first counterclockwise and then clockwise back to its home position (FIG. 1). As illustrated in FIG. 1, a cam lever 25, secured on such rear drive shaft 24, is also rocked first counter-clockwise and then clockwise during a machine operation. With such counter-clockwise rocking of the cam lever 25, a stud 26 thereon strikes a tail portion 23a of the operating arm 23, shifting the bail 21 and the previously rocked interponent 20 toward a lower step 18a of the hammer latch 18, which thereby is moved clockwise near mid-cycle of a machine operation. As best understood from FIG. 1, such clockwise movement of the hammer latch 18, which is rockably supported by a further shaft 27 extending between the printer side frames 12, releases the associated print hammer 10 to the action of a strong spring 30 arranged so as to continually urge such hammer clockwise about the support shaft 11. As illustrated in FIG. 2, this causes the print hammer 10 to be impelled against that type member 17 which is positioned at the printing line. lthough not illustrated herein, the usual journal or other record tape extends between the platen 16 and type member 17 for receiving the selected printed indicia thereon.

Restoring of the print hammer 10 to its cocked positionthat is, from that position illustrated in FIG. 2 to that position illustrated in FIG. 1, is through engagement thereof by bail 28 being returned to a home position just prior to the end of a machine operation. Such bail 28 extends between the free end portions of a pair of hammer restoring arms 29 carried by the hammer support shaft 11, which arms 29, through the usual oscillating movement imparted to the operating arms 23 by rocking of the rear drive shaft 24, are first caused to rock a precise distance clockwise prior to mid-cycle of a machine operation, where the upper bail 28 thereof frees the print hammer for a full (printing stroke) clockwise movement (FIG. 2), and are then caused to be returned counter-clockwise to home prior to the end of a machine operation, where the upper bail 28 thereof positively restores the print hammer 10 to its cocked position (FIG. 1).

With such overall construction and mode of operation, it is apparent that when the hammer 10 makes its printing stroke under normal tension of the strong spring 30, sharp contact thereof with the selected ty'pe member 17, the normal reaction of the usual type member spring 17a urging same away from the platen 16, and the type members driving force against the resiliency of the platen 16 all cause said hammer 10 to rebound sharply. That is, while the spring 30 is pretty well spent as of the time the print hammer 10 effects an impression on the machine journal or record tape (FIG. 2), a slight re-stretching of such spring 30 is had at the end of each printing stroke completed by the hammer 10, which,-upon contraction, will tend to cause such hammer 10 to make a second light impression stroke against the type member 17 shifted to the printing position. This second light impression stroke, commonly referred to as a rebound stroke, generally results in a blurring or smudging of the first impression made on the journal or other record material. It is the elimination of this undesirable condition which the present invention overcomes through use of a single pawl associated with each of the print hammers 10, all in the manner described hereinafter.

Improved Anti-Rebound Mechanism As disclosed in FIG. 1, each of the printer side frames 12 is supported both by the previously-described machine rear drive shaft 24 and by a second shaft 31 fixedly extending laterally across the machine. Rotatably mounted on such fixed shaft 31, adjacent each print hammer 10, is an anti-rebound pawl 32, having an upwardly extending arm portion 33 and a rearwardly extending tail portion 34. A spring 35, stretched between such pawl arm portion 33 and an appropriate hanger 36 carried by a further shaft 37 extending laterally across the machine, yieldingly urges the pawl 32 counter-clockwise that extent permitted by the upper surface of the pawl tail portion 34 coming into engagement with the under surface of a square stud 38 carried by the print hammer 10. As illustrated, the pawl tail portion 34 is arcuately shaped and has the inner end portion of its upper surface, designated as 34a, developed on a common radius which, until the square stud 38 is caused to leave same during each printing stroke of the hammer 10, maintains the pawl 32 in what may be called an ineffective position with respect to stopping the hammer 10 from striking an aligned type member 17. That is, as best understood from FIG. 1, the normal positioning of the anti-rebound pawl 32 by the print hammer carried square stud 38, when such print hammer is in its cocked position, is maintained by surface 34a throughout the major portion of each printing stroke made by the hammer. The outer end of such pawl tail portion 34, being of a length slightly greater than that of the square stud 38, is provided with an upper surface 34b defined by a lesser radius than that of the inner surface 34a, which surface 3415 would,

when considered in conjunction with the print hammer 10, permit the spring 35 to rock the anti-rebound pawl 32 slightly counter-clockwise from the positioning thereof in FIG. 1until the surface 34b comes into contact with the under surface of the hammer carried stud. 38.

Intermediate such pawl tail surfaces 34a and 34b is a recessed zone 34c of the pawl tail portion 34, being again of a length greater than that of the square stud 38, being squared at that end thereof merging into the surface 34b, and being inclined at that end thereof merging into the surface 34a. The overall effect of such configuration of the pawl 32 is that of a hook member having a major length (34a) of one radius, a minor length (34b) of a lesser radius, and an undercut or recess (34c) therebetween with one square wall and one sloping Wall.

The overall operation of such an anti-rebound pawl 32 with respect to its associated print hammer 10 is as follows. As set out above, normal positioning of the pawl 32 is that as illustrated in FIG. 1, where the upper surface 34a of the pawl tail portion 34 is, through normal tension of the spring 35, maintained in engagement with the hammer stud 38. Upon release of the print hammer 10 from its cocked position, in that precise manner described hereinabove, stud 38 thereof is immediately driven along the overall length of the surface 34a, and, in view of the great weight of the hammer spring 30, is permitted to strike the selected type member 17 (as illustrated in FIG. 2) prior to the time that any appreciable extent of counter-clockwise rocking movement is imparted to the anti-rebound pawl 32 through tension of its associated spring 35. That is, although the spring is free to rock such pawl 32 as soon as the square stud 38 leaves engagement with surface 340:, the great speed of travel of the print hammer 10 during its printing stroke will actually permit such stud 38 to clear the pawl recess 34c and be positioned above the pawl surface 34b by the time that spring 35 causes the pawl 32 to next engage the under surface thereof. This operation, which may be termed a ski-jumping of the hammer carried square stud 38 from the pawl surface 34a to the pawl surface 34b during a printing stroke is best understood from FIG. 2. Essentially, the jumping-over of the pawl recess 340 by the square stud 38 during each printing stroke of the hammer 10 is the result of the combined variations both in the weights of the springs 30 and 35 and in the planes of the pawl surfaces 34a and 3412.

Looking now to the illustration in FIG. 3, when the print hammer 10 recoils from its impact with the selected type member 17, all in the manner explained above, the square stud 38 thereof will move backward and off the surface 34b of the pawl tail portion 34 and into alignment with the recess 34c therein, in turn permitting the pawl 32 to rock further counter-clockwise by the spring 35 to the position shown. This presents the squared wall of the recess 340 in the path of the square stud 38 to positively block any attempted rebounding movement of the print hammer 10. Since the strong spring 30 is almost spent at this time, no additional (partial) printing stroke of the hammer 10 can be completed thereby before the spring 35 has had time to impart sufiicient rocking movement to the pawl 32 for presenting the recess 340 in its hammer blocking position.

As mentioned above, restoring of the print hammer 10 to its cocked position (FIG. 1) takes place during the second half-cycle of a machine operation, which is when the upper bail 28 is returned from that position of FIG. 2 to that position of FIG. 1. When this happens, as can be understood from FIG. 3, the hammer carried square stud 38, when engaging the inclined wall of the pawl recess 34c, will cam the pawl 32 again to its normal, ineffective position. Of course, such positioning of the pawl 32 will be had as long as the stud 38 maintains engagement with the upper surface 34a of the pawl tail portion 34.

Although not so illustrated herein, it is axiomatic that the instant anti-rebound pawl 32, or one of a quite similar construction, will be just as effective in its operation if same is mounted in a reversed mannerthat is, with its surfaces 34a, 34b and recess 34c adapted to engage the upper surface of hammer stud 38. Complete operation of the pawl 32 would then be had solely by gravity-due to the sheer weight thereof. This reversal in the mounting of such a pawl 32, and, of course, also in the stud engaging surfaces and recess thereof, is desirable for those printer constructions not having available either the shaft 37 or the space for a tension spring 35. Thus, while the form of mechanism herein shown and described is admirably adapted to fulfill the objects primarily stated, it is to be understood that it is not intended to confine the invention to that one form of embodiment precisely disclosed, for it is susceptible of embodiment in various other forms, all coming within the scope of the following claims.

What is claimed is:

1. The combination of a print hammer; a type carrier; means imparting a printing stroke of said hammer with respect to said type carrier for taking an impression therefrom; an abutment on said print hammer; and a unitary pawl member operably associated with said abutment for preventing the print hammer from taking more than one impression from said type carrier during each printing stroke thereof; said pawl member having a control surface cooperating with said abutment throughout a major portion of each printing stroke of the print hammer for maintaining the pawl member ineffective; and said pawl member having a latching surface cooperating with said abutment immediately following the completion of each printing stroke of the print hammer for making the pawl member then effective for restraining said print hammer in a partially retracted position.

2. The structure of claim 1 in which said printing stroke imparting means comprises a spring for impelling the print hammer against said type carrier; said latching surface defines one wall portion of a latch member carried recess; said control surface comprises a first surface portion extending to said recess and a second surface portion extending therebeyond; means for urging both said control surface and said recess toward engagement with said hammer abutment; said control surface first surface portion normally engaging said hammer abutment; and said hammer impelling spring is of a magnitude suflicient to transfer the hammer abutment along said control surface first surface portion, across said recess, and onto said control surface second surface portion during each printing stroke of the print hammer, after which printing stroke the magnitude of said spring decreases to an extent which permits the said recess to engage the hammer abutment during any print hammer rebound from the type carrier.

3. The structure of claim 2 in which the control surface second surface portion is in a plane varying from the plane of the control surface first surface portion.

4. The structure of claim 3 in which said means for urging both said control surface and said recess toward engagement with said hammer abutment is of a magnitude lesser than that of the hammer impelling spring prior to and during each printing stroke of the print hammer, with the magnitudes thereof being reversed thereafter.

5. The combination of a print hammer; a type carrier; means imparting a printing stroke to said print hammer with respect to said type carrier for taking an impression therefrom; a projection on said print hammer; and a unitary pawl member for preventing the print hammer from taking more than one impression from said type carrier during each printing stroke thereof; said pawl member having, one behind another and in the direction of the printing stroke, a first control surface, a latching surface, and a second control surface, all adapted to engage said hammer projection; each of said first and second control surfaces, when engaged with said projection, permitting the print hammer to take an impression from the type carrier; said latching surface, when engaged with said projection, preventing the print hammer from taking an impression from the type carrier; said projection normally engaging the first control surface and maintained in engagement therewith throughout the major portion of each printing stroke of the print hammer; and said print hammer operating at such a speed in the printing stroke to cause said projection to skip over said latching surface and move directly from said first control surface to engagement with the second control surface, after which printing stroke rebound of the print hammer is effective for moving said projection from said second control surface and into engagement with the latching surface.

6. The structure of claim 5 in which said printing stroke imparting means comprises a strong spring for impelling said print hammer against said type carrier; and a further spring of lesser strength continually urges said pawl member in a direction for maintaining one or the other of the control and latching surfaces thereof in engagement with the print hammer projection.

References Cited in the file of this patent UNITED STATES PATENTS 1,613,129 Robertson Jan. 4, 1927 1,652,057 Shipley Dec. 6, 1927 1,747,743 Sundstrand Feb. 18, 1930 2,066,784 Lake et al. Jan. 5, 1937 2,117,451 Robertson May 17, 1938 2,204,187 Ostler June 11, 1940 2,342,082 Klosterman Feb. 15, 1944 

1. THE COMBINATION OF A PRINT HAMMER; A TYPE CARRIER; MEANS IMPARTING A PRINTING STROKE OF SAID HAMMER WITH RESPECT TO SAID TYPE CARRIER FOR TAKING AN IMPRESSION THEREFROM; AN ABUTMENT ON SAID PRINT HAMMER; AND A UNITARY PAWL MEMBER OPERABLY ASSOCIATED WITH SAID ABUTMENT FOR PREVENTING THE PRINT HAMMER FROM TAKING MORE THAN ONE IMPRESSION FROM SAID TYPE CARRIER DURING EACH PRINTING STROKE THEREOF; SAID PAWL MEMBER HAVING A CONTROL SURFACE COOPERATING WITH SAID ABUTMENT THROUGHOUT A MAJOR PORTION OF EACH PRINTING STROKE OF THE PRINT HAMMER FOR MAINTAINING THE PAWL MEMBER INEFFECTIVE; AND SAID PAWL MEMBER HAVING A LATCHING SURFACE COOPERATING WITH SAID ABUTMENT IMMEDIATELY FOLLOWING THE COMPLETION OF EACH PRINTING STROKE OF THE PRINT HAMMER FOR MAKING THE PAWL MEMBER THEN EFFECTIVE FOR RESTRAINING SAID PRINT HAMMER IN A PARTIALLY RETRACTED POSITION. 